Motor device whose circuit, comprises a thin layer of hard magnetic material

ABSTRACT

Micro-motor with a homopolar structure, comprising a coil on the base on which a tubular core is fitted, a second tube fitted on a pole piece carrying a pinion, these two tubes being fitted one in the other, and a rotor comprising a bell with a thin cylindrical wall made of hard magnetic material.

D United States Patent 1 1 1111 3, Oudet 1451 Aug. 21. 1973 1 MOTORDEVICE WHOSE CIRCUIT, [56] References Cited COMPRISES A THIN LAYER OFHARD UNITED STATES PATENTS MAGNETIC MATERIAL 1 3,539,845 11/1970Stcherbatcheffw, 310/156 x Inventor; Claude Michel oudet Begancon3,469,124 9/1969 WiilCOX 310/266 X France 3,508,091 4/1970 Kavanaugh310/257 X [73] Assignee: Societe Civile de Recherches en PrimaryExaminer D R Duggan Mntiere de micro-moteurs electriques An""""LI'hW "MH "'"C (1 K t t S.0.C.R.E.M., Paris, France Omey o n a 0y mgh e a [22]Filed: May 10, 1972 [57] ABSTRACT [21] Appl. No.: 252,116 Micro-motorwith a homopolar structure, comprising a coil on the base on which atubular core is fitted, a second tube fitted on a pole piece carrying apinion, these i 310/156 310/ 2 6 1 262; two tubes being fitted one inthe other, and a rotor I I n u I I I n 0 a a I o I I a I In! u I I I I Iu u n n I a I e u I e n I I v I b l l d 581 Field of Search 310/156,266, 257, a mm a wan ma 8 hard magnetic material.

4 Claims, 3 Drawing Figures Patented Aug. 21 1973 3,754,155

2 Sheets-Sheet 1 Patented Aug. 21, 1973 3,754,155

CD I r-4 MQTOR pEvlCE WHOSE CIRCUIT, COMPRISES A THIN LAYER or. HARDMAGNETIC MATERIAL The invention relates to the micro-motors used, inparticular, in watch-making applications, and designed tooperate by thestep by step method.

In the prior US. Pat. No. 3,539,845, filed on Nov. I0, 1970, in the nameof Georges Stcher-batcheff, for Motor whose magnetic circuit comprises athin layer of hard magnetic material, there is disclosed, in particular,a micro-motor of this kind with a homopolar structure: the rotorconsists of a bell with a cylindrical portion made of hard magneticmaterial, while the stator comprises two pole pieces each fitted with ahomopolar pinion, these two pinions respectively being pola'rizedpositively and negatively by the current which flows in the coil, andtheir facing teeth define a gap in which said cylindrical portion isplaced. The latter is magnetized with alternately positive and negativepolarities in the same step as the pinions of the stator.

In accordance with a basic characteristic of the U.S. patent abovereferred to, the magnetization is radial, the flux being substantiallyperpendicular to said cylindrical portion, and the thickness of thelatter is such that the ratio x of the product I-l .L of the coercivefield through said thickness to the product B,.e of the remanentinduction through the dimension of the gap is substantially less thanone, preferably at least equal to 0.1.

In the U.S. patent above referred to, it was explained that this use ofa magnetically hard thin layer" makes it possible considerably to reducethe residual torque C of the motor in the absence of current, withoutthereby notably reducing the torque C due to the current. This residualtorque is usually considerable in this kind of polarized, motor whereinthe flux of the magnet traverses the coil and, reciprocally, the fluxdue to the current traverses, the magnet. The result is that it isusually very difficult to make these motors work step by step when onlya very small number of ampere-turns is available. The U. S. Pat. abovereferred to describes, not only means of reducing C (the chief of whichis the use of the thin layer) but also means of superimposing on thisinevitable natural residual torque, an artificial at rest torque with acomponent C at a frequency double that of C and, in the important casewhere it is desired to. operate the motor by means of current impulseswith a constant signal, a component C at the. frequency of the current,these two components having to have a clearly defined phase in relationto; that of C The present invention offers a further 'means of improvingthe step by step working of a motor of this kind andof increasing itsoutput.

In accordance with the invention, the polar piece of the statorwhichcarries the inside pinion is carried at the end of a tube made ofsoft magnetic material, and

this tube is fitted telescopically inside another tube made of softmagnetic material which constitutes the core of the coil. In accordancewith, a preferred method of embodiment, the other polar piece of thestator does not comprise any pinion and consists of a smooth ring madeof magnetically soft material fitted on a base, also made ofmagnetically soft material, on which said core is itself fitted.

Other peculiarities, as well as the advantages of the invention, willemerge clearly from the following description. In the attached drawings:

FIG. 1 is a half-section along the line I-l in FIG. 2 of a micro-motorin accordance with a preferred mode of embodiment of the invention,shown in the drawing on a greatly enlarged scale.

FIG. 2 is a half-section along the line IIII in FIG. 1.

FIG. 3 is a half-section along the line III-Ill in FIG. 1.

FIG. 1 shows that this motor comprises a coil 1 connected to a feedconductor 2 which traverses its base 3. On the latter are fitted, on theone hand a tube.4 which constitutes the core of the coil, and on theother hand a ring 5 with a smooth inside wall, terminated at the top bya bearing support 50 and not comprising any pinion.

A second tube 6 is fitted on a polar piece 7 which carries a pinion 7a(also shown in FIG. 3). The assembly is done in the following manner:

' The unit 6-7 on the one hand, and the unit 3-4 on the other hand, arefirst annealed separately at high temperature, which practically weldsthe assembled parts.

Then, the two tubes 6-4 are slipped one into the other, with a play ofabout 10 microns. This assembly makes it possible to orient themperfectly perpendicularly to the base. The magnetic joint formed has alarge surface.

The bell 9 which constitutes the rotor is integral with a shaft 10.

Moreover, in accordance with the technique described in the copendingUS. patent application filed in the names of Georges Stcherbatcheff andClaude Oudet on May 12, 1972 for: Method and devices for adapting amonophase synchronous motor to step by step working," artifical at rest"torques have been devised by mens of a polarized system which has noeffect on the magnetic circuit of the part of the motor just described.

This polarized system is made up of a permanent magnet 11 and a toothedwheel 12.

' The magnet 11 is fixed inside the ring 5, above the bell 9, and itcomprises poles, represented by thickened lines (such as 11a) in FIG. 2.

These poles are equal in number to the teeth of the pinion 7 andalternately positive and negative.

The wheel 12, made of soft magnetic material, is wedged at the top endof the shaft 10 above the bell 9.

FIG. 2 shows that the teeth 12a which it comprrises are equal in numberto the poles of the magnet 11 (i.e.: 8 in the non-limiting exampledescribed).

It is clear that this polarized system is identical to that which hasbeen shown in unbroken lines in FIGS. 1 and 2 of the above-mentionedpatent application (magnet 3 cooperating with the toothed wheel 2).

The law of torque thus takes the fonn illustrated in FIG. 3 of saidapplication, with the advantages which have been explained therein.

It goes without saying that various modifications of I detail may bemade to the motor described, without departing from the spirit of theinvention.

In the present text, as well as in the attached claims, H is expressedin Oersted units and B in Gauss units.

I claim:

l. Micro-motor of the type comprising a rotor with a cylindrical portionmade of hard magnetic material and a stator comprising two polar piecesrespectively polarized positively and negatively by the current whichflows in a coil, these polarized pieces defining an air gap in whichsaid cylindrical portion is placed and one at least of these two polarpieces is fitted with a set of substantially equispaced salient statorpoles, said cylindrical portion being magnetized radially and being ofsuch thickness that the ratio x of the product l-l,,.L, H being thecoercive field of said hard magnetic material and L the value of saidthickness, to the product B,.e, B, being the remanent induction and ethe dimension of the said air gap, is substantially below unity,characterized by the fact that the polar piece of the stator whichcarries the said set of stator poles is carried at the end of a tubemade of soft magnetic material, this tube being fitted telescropicallyinside a further tube made of soft magnetic material which constitutesthe core of the coil.

2. Micro-motor in accordance with claim 1, further comprising a base onwhich said core is fixedly mounted, the said tube forming a magneticjoint with the said set of stator poles and the said core forming afurther magnetic joint with the said base, the said magnetic jointsbeing of the type having a negligibly small reluctance resulting fromannealing at high temperature.

3. Micro-motor in accordance with claim 1, characterized by a polarizedsystem consisti g of an annular permanent magnet fixed above saidcylindrical portion and by a toothed wheel made of soft magneticmaterial wedged on the shaft of the rotor, facing said magnet whichencircles it.

4. Micro-motor in accordance with claim 3, chaaracterized in that saidmagnet comprises alternate poles equal in number to the number of teethon said wheel and to the number of stator poles of the said set.

1. Micro-motor of the type comprising a rotor with a cylindrical portionmade of hard magnetic material and a stator comprising two polar piecesrespectively polarized positively and negatively by the current whichflows in a coil, these polarized pieces defining an air gap in whichsaid cylindrical portion is placed and one at least of these two polarpieces is fitted with a set of substantially equispaced salient statorpoles, said cylindrical portion being magnetized radially and being ofsuch thickness that the ratio x of thE product Hc.L, Hc being thecoercive field of said hard magnetic material and L the value of saidthickness, to the product Br.e, Br being the remanent induction and ethe dimension of the said air gap, is substantially below unity,characterized by the fact that the polar piece of the stator whichcarries the said set of stator poles is carried at the end of a tubemade of soft magnetic material, this tube being fitted telescropicallyinside a further tube made of soft magnetic material which constitutesthe core of the coil.
 2. Micro-motor in accordance with claim 1, furthercomprising a base on which said core is fixedly mounted, the said tubeforming a magnetic joint with the said set of stator poles and the saidcore forming a further magnetic joint with the said base, the saidmagnetic joints being of the type having a negligibly small reluctanceresulting from annealing at high temperature.
 3. Micro-motor inaccordance with claim 1, characterized by a polarized system consistingof an annular permanent magnet fixed above said cylindrical portion andby a toothed wheel made of soft magnetic material wedged on the shaft ofthe rotor, facing said magnet which encircles it.
 4. Micro-motor inaccordance with claim 3, chaaracterized in that said magnet comprisesalternate poles equal in number to the number of teeth on said wheel andto the number of stator poles of the said set.